CT overcomes many problems faced by using conventional two-dimensional radiographs. CT does this by scanning thin slices of the object with a narrow X-ray beam that rotates around the object. This produces an image of each slice as a cross-section of the body, for example, and can thus show each of the tissues or objects in a slice of width ranging from 0.5 mm-10 mm, with 5 mm being typical.
In contrast to radiography, CT can also differentiate between tissues or objects of similar density because of the narrow x-ray beam and the use of “windowing.” In CT, information acquired can be stored on a digital computer as digital raw data and an image can, for example, be displayed on a video monitor or printed onto x-ray film. Such an image is made up of a matrix of thousands of tiny squares or pixels. A conventional single slice CT image has 262,144 pixels arranged in an array of 512×512 pixels, and 1,048,576 pixels (known as a “Megapixel”) arranged in an array of 1024×1024 pixels is fast becoming common.
The detection of contraband in transportation containers, and particularly in to larger containers such as ocean freight cargo containers, air freight cargo containers, etc., presents a long-standing problem. Only a small percentage of such cargo containers are inspected for contraband, such as illegal drugs, explosive devices, illegal weapons, radioactive materials, etc. As a result, such containers present an inviting vehicle for the smuggling of contraband.
When such containers are inspected for contraband, it usually is very labor-intensive and time-consuming to do so. Therefore, it also is relatively expensive to do so. These factors are significant in limiting the amount of inspection which can be done at a tolerable cost.
Accordingly, one of the objects of the invention is to provide a system or device and method for inspecting transportation containers for contraband at a relatively modest cost.
CT scanners are used to perform the non-invasive inspection of objects such as luggage, bags, briefcases, cargo containers, vehicles and the like, to identify hidden contraband at airports, public buildings, roadways and other security checkpoints. The contraband may include hidden guns, knives, explosive devices and illegal drugs, for example.
Computed tomography (“CT”) enables the reconstruction of the cross-sectional images of the cargo contents being scanned, enabling identification of the items in the container. CT images have long attracted much attention in the field of medical diagnosis because they provide a sharp tomographic image of a soft tissue which could not be obtained using conventional X-ray films. CT images also provide higher resolution, better image contrast and greater sensitivity to characteristics of the object being scanned, than radiographs.
While the smuggling of contraband such as guns and explosives onto planes in carry-on bags and in luggage has been a well known, ongoing concern, another serious threat is the smuggling of contraband across land borders by concealment in trucks or automobiles and by boat in large cargo containers. Standard cargo containers are typically 20 to 50 feet (6 to 14 meters) long, 8 feet (2½ meters) high and 6 to 9 feet (3 to 4 meters) wide. Air cargo containers, which typically contain many pieces of luggage or other cargo to be stored in the is body of an airplane, may range in size from about 35 by 21 by 21 inches (around less than 1 meter by 0.7 meter by 0.7 meter) up to about 240 by 118 by 96 inches (6 by 3 by 2½ meters).
Large collections of objects, such as, for example, many pieces of luggage, may also be supported on pallets. Pallets, which may have supporting side walls, may be of a size comparable to cargo containers.
Typical airport scanning systems for carry-on bags have tunnel entrances up to about 0.40×0.40 meters. Scanning systems for checked luggage have only slightly larger openings. Thus, such systems are insufficient to inspect cargo containers because only bags that are small enough to fit through the scanner's tunnel may be inspected. The relatively low energies used in typical X-ray luggage and baggage scanners usually are insufficient to enable the X-rays to pass through the much larger cargo containers. In addition, many such conventional systems operate too slowly to economically inspect larger objects, such as cargo containers. Thus, the art faces a problem in developing a system for scanning large objects efficiently and accurately.